Transport mechanism of furosemide in perilymph and endolymph of guinea pig

Abstract

Using HPLC, the concentrations of furosemide, one of the organic anions, in the perilymph and endolymph of the guinea pig cochleae were measured after intravenous administration of 100mg/kg of furosemide. We further investigated the furosemide concentrations in the perilymph and endolymph pretreated with the organic anion transport inhibitor, probenecid.
In the scala tympani perilymph (STP), a peak concentration of 4.9μg/ml was reached at 15min. after injection of furosemide and gradually declined thereafter. The concentration of furosemide increased slowly and continued to rise gradually in the scala vestibuli perilymph (SVP).
In the endolymph, the concentration of furosemide increased slowly for one hour to 1.6μg/ml and gradually declined thereafter.
Two hundred mg/kg of probenecid had no effect on the furosemide elimination in the endolymph except the furosemide concentration at 2hr, though the elimination curve of furosemide in STP was drastically changed and became analogous to that in SVP which was unaffected by probenecid. The effect of probenecid in the endolymph was very similar to that in the serum, while the pronounced gradient of the furosemide concentration existed between them.
These results suggest that the furosemide is passively transferred from blood to the endolymph with relatively high impenetrability.